Transitional Phase - Between wakefulness and sleep. This lasts for one to seven minutes and is 5% of the total sleep time.

Light Sleep Phase - This is 50% of the total sleep time.

Slow Wave Phase (Delta Phase) - A deeper and more relaxed sleep associated with 20% of the total sleep time.

RAPID EYE MOVEMENT (REM)

This is a period of deep, refreshing sleep. Eyes move side to side and the skeletal muscles are nearly paralyzed which results in a loss of muscle tone in the upper airway. This represents 25% of the total sleep time and is the stage where dreaming occurs.